This, in turn, speeds up time to market and contributes towards lower assembly and manufacturing costs through improved use of equipment for the supply chain. This strategy can be employed for both existing and new turbine models.
A common strategy typically uses one turbine platform for several sister models, using the same power rating and various rotor blade lengths.
Another variation can see one turbine platform used for sister models, each offering a variety of power ratings and matching rotor lengths to optimise yield for different wind classes. The Repower XM-series, for instance, comprises three sister models of 3.4MW, 3.2MW and 3MW each with matching rotor blade sizes of 104 metres, 114 metres and 122 metres respectively.
A third strategy uses different turbine platforms, and shares a common rotor blade diameter, combined with two or more different power ratings.
An example of this strategy is the production of one rotor blade length for the Nordex N117/2400 Gamma and the N117/3000, which was introduced this year on the new Delta turbine platform. Having also a similar aerodynamic shape, these two blades can be manufactured using the same moulds.
Spanish supplier Gamesa applies two of these strategies in the 2-2.5MW power-rating class. The company's 2MW turbine dates back to 2002, and the initial 80-metre rotor blade was later expanded to 87-metre, 90-metre and 97-metre diameters.
Now, a new sister turbine has been added — the G114-2.0MW, an IEC class IIIA turbine. This introduces a 114-metre rotor diameter for a record-low 196W per square metre specific power rating. A prototype is planned to be ready in the autumn.
Also in development in this platform is a new 2.5MW turbine model that will use a similar 114-metre diameter rotor blade. A G114-2.5MW prototype is planned for June or July 2014.
Gamesa's product development director, Antonio de la Torre, said that the modular design is a key product development driver. Offering some historic context, he explained that a new generation of blade airfoils was developed for the G97-2.0MW, launched in 2010, with a parallel design focus on manufacturability and high aerodynamic performance.
This G97 blade contains carbon fibres at highly stressed structural sections, he says, yet performs like other long blades producing 100-metre diameter.
"This G114 blade builds further on G97 experiences," said de la Torre. "The main overall changes were a switch to glass-fibre reinforced epoxy composite, skipping carbon and introducing a new manufacturing process based upon vacuum infusion technology. Most importantly, with this G114 blade we succeeded in lowering manufacturing costs, while aerodynamic performance is comparable to competitor blades of 120-metre rotor size," he said.
Different but the same
Despite being structurally different due to different wind classes, the G114-2.0MW and G114-2.5MW aerodynamic blade are similar in shape, enabling Gamesa to use the same moulds for manufacturing.
Another focus area for the G114-2.5MW is to benefit from drivetrain modularity characteristics between the 2.0MW and 2.5MW series.
"Gamesa develops and manufactures its own gearboxes and generators in-house," said de la Torre. "In the past we have put a lot of effort into drivetrain reliability enhancement. This has resulted in almost zero failures for our 2MW class gearboxes, and the combined mechanical and electrical/power-electronic experiences especially with our most advanced G97 model were fed into the G114-2.5MW development."
The G114-2.5MW again features the drivetrain concept from the 2MW series. It incorporates a main shaft with two bearings, a three-stage gearbox and doubly fed induction generator (DFIG), while a permanent magnet generator is an option, he added.
This focus on modularity for main drive components and systems allows Gamesa engineers to achieve comparable reliability in the drivetrain performance for the G114-2.5MW despite being new and higher rated.
De la Torre said: "At the main component and systems level, we put a great deal of effort and resources into advanced simulation and validation during all of the development stages of the product, and well before installing the prototype.
"Because all components and systems have already been tested and validated, a standard assessment is largely all that is left for turbine certification. A related benefit is that time-to-market can be substantially shortened as well."
The G114-2.5 is envisaged to compete mainly with other turbines in the 2.4-3MW-plus class, initially focused at Europe, the US, and later Brazil too.